Theory and simulation of optomechanical effects in phoxonic crystals

Phoxonic crystals are periodic structures that can exhibit dual phononic and photonic band gaps, thus allowing the simultaneous confinement of both acoustic and optical waves inside the same defect such as a cavity or a waveguide. Then, one can expect an enhancement of the phonon-photon interaction for the purpose of novel optomechanical devices, in particular for the modulation of light by acoustic waves. We study theoretically the optomechanic interaction in different (2D[1], slabs[2], and strips phoxonic crystals cavities. We take into account both mechanisms that contribute to the acousto-optic interaction, namely the photoelastic and moving interface effects. The strength of the acousto-optic coupling is evaluated for each phonon-photon pair by calculating either the modulation of the photonic frequency by the acoustic mode or the so-called coupling rate. The contributions of the photoelastic and moving interfaces effects can have similar or very different magnitudes. Moreover, they can be in phase and add together or be out of phase and partly cancel each other. We can notice that, due to symmetry reasons, only acoustic modes having a specific symmetry can couple to photonic modes. Finally, we discuss the influence of the material properties as concerns the photoelastic effect [1] since the latter strongly changes when the optical frequency approaches the energy of the direct band gap. [1]S Eljallal et al JPCM 26, 015005(2014) [2]S Eljallal et al PRB 88, 205410(2013)